Chronic pain is a significant public health problem for which current therapies are inadequate. The development of improved treatments for pain will require a better understanding of the fundamental mechanisms by which nociceptive neurons are activated or inhibited. A growing body of evidence suggests that activation of skin keratinocytes by thermal, chemical, or mechanical stimuli could result in activation or inhibition of adjacent epidermal nocieptor terminals, and that such signaling might exhibit specificity among basal vs. superficial keratinocyte layers. A major hurdle to addressing these possibilities definitively is the lack of a means of selectively stimulating keratinocytes without simultaneously stimulating nociceptors, themselves. In this proposal, we outline a plan to selectively express, within transgenic mouse keratinocytes, ion channel receptors (TRPV1 and channelrhodopsin) that can be uniquely activated by chemical and/or light stimuli. Activation of these receptors in the intact mouse will allow us to determine whether keratinocyte stimulation is sufficient to trigger pain-related behaviors and signaling to the spinal cord. Furthermore, by precisely regulating the expression patterns of these channels in discrete epidermal layers, we will be able to establish how the consequences of signaling from keratinocytes differ across the basal to apical spectrum of the epidermis. Success in these aims will provide us with a clearer understanding of the role of keratinocytes in the initiation and control of pain, as well as powerfl new tools that will in the future allow us to guide the rational development of improved therapies for pain. PUBLIC HEALTH RELEVANCE: We seek to understand how non-neuronal skin cells help the nervous system detect and respond to painful environmental stimuli. A better understanding of this communication within the skin will aid the development of improved drugs to fight chronic pain that lack the unwanted side effects that limit the usefulness of currently available pain medications.